Fluoran compounds, crystalline toluene adducts thereof, recording material comprising same and process for their preparation

ABSTRACT

Disclosed are novel fluoran compounds represented by the formula (I):    &lt;IMAGE&gt;  (I)  wherein R1 and R2 are different groups selected from cyclohexyl, n-butyl and isobutyl, e.g., in the form of crystals characterized by a specific X-ray diffraction diagram; crystalline toluene adducts thereof; and recording materials containing these fluoran compounds.

This is a division of application Ser. No. 07/553,834, filed Jul. 18,1990, now U.S. Pat. No. 5,220,038.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to novel fluoran compounds which areuseful as chromogenic compounds in recording materials such as pressuresensitive and heat-sensitive recording materials. More particularly, theinvention relates to crystal of a fluoran compounds in crystalline form,to crystalline toluene adducts thereof, to a process for the preparationof these compounds and to recording materials comprising thesecompounds.

2) Description of the Prior Art

Pressure-sensitive recording, heat-sensitive recording andelectroheat-sensitive recording have conventionally been used as systemsfor recording transfered information through the mediation of externalenergy, such as pressure, heat or electricity, by utilizing a colorreaction between a colorless or pale colored electron donative compound(chromogenic compound) and an organic or inorganic electron acceptor(developer).

In these systems, fluoran compounds have widely been used as thechromogenic compound.

Many fluoran compounds are known in the prior art, including thosehaving structures similar to the fluoran compounds of the invention, forexample, those having the formulas (A), (B), (C), (D) and (E). ##STR2##Japanese Patent Laid-Open Publication SHO 48-43296(1973) ##STR3##Japanese Patent Laid-Open Publication SHO 48-43296(1973) Japanese PatentLaid-Open Publication SHO 60-202155(1985) ##STR4## Japanese PatentLaid-Open Publication SHO 48-23204(1973) ##STR5## Japanese PatentLaid-Open Publication SHO 54-34909(1979) ##STR6## Japanese PatentLaid-Open Publication SHO 59-197463(1984)

However, the compound of the formula (A) has the disadvantage of verylow solubility in capsule oil when the compound is used in apressure-sensitive recording material. Additionally, in the case ofapplying to the heat-sensitive recording material, the compound has thedefect that the compound itself colors gray to dark gray when mixed witha developer such as bisphenol A and provide only a gray to dark graycolored (soiled) paper by applying the mixture to a paper.

The chromogenic temperatures of the compounds of formulas (B), (C), (D)and (E) are too high to permit their use in a heat-sensitive recordingmaterial. Consequently, the performance of these prior art compoundscannot fully meet the present market demand for more rapid and higherdensity recording. Therefore, a chromogenic compound capable of quicklydeveloping color at a lower temperature has been strongly desired.

Further, the compounds of formulas (A)-(E) are poorly soluble in capsuleoil and their performance is still unsatisfactory for thepressure-sensitive recording material.

OBJECTS OF THE INVENTION

One object of the present invention is to provide novel fluorancompounds capable of meeting the current performance demands as achromogenic compound for use in the recording materials.

Another object of the present invention is to provide crystalline formsof novel fluoran compounds having further improved functional propertieswhen used in recording materials.

A further object of the present invention is to provide a process forthe preparation of the novel fluoran compounds and specific crystallineforms of these compounds.

Still another object of the present invention is to provide recordingmaterials comprising a novel fluoran compound of this invention,especially those comprising a specific crystal form of the compound.

SUMMARY OF THE INVENTION

In a composition aspect, the present invention relates to novel fluorancompounds represented by Formula (I): ##STR7## wherein R₁ and R₂ aredifferent groups selected from cyclohexyl, n-butyl and isobutyl.

In a process aspect, this invention relates to a process for thepreparation of the fluoran compounds of this invention by reacting abenzoic acid derivative represented by Formula (II): ##STR8## wherein R₁and R₂ are the same as in Formula (I), with a diphenylamine derivativerepresented by Formula (III): ##STR9## wherein R₃ is a lower alkylgroup.

In other composition aspects, this invention relates to the fluorancompounds of this invention in crystalline form, which crystals arecharacterized by a specific X-ray diffraction diagram and is representedby Formula (I); to crystalline solvated adducts, e.g., toluene adducts,of the fluoran compounds of this invention, which crystals arecharacterized by a specific X-ray diffraction diagram; and to recordingmaterials comprising a fluoran compound or specific crystal orcrystalline toluene adducts of a fluoran compound of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, FIG. 1 is an X-ray diffraction diagram of a Type Icrystal of the compound represented by Formula (I-1); FIG. 2 is an X-raydiffraction diagram of a Type II crystal of the crystalline tolueneadduct of the compound represented by Formula (I-1); FIG. 3 is an X-raydiffraction diagram of a Type III crystal of the compound represented byFormula (I-2), FIG. 4 is an X-ray diffraction diagram of a Type IVcrystal of the crystalline toluene adduct of the compound represented byFormula (I-2), FIG. 5 is an X-ray diffraction diagram of a Type Vcrystal of the compound represented by Formula (I-3), FIG. 6 is an X-raydiffraction diagram of a Type VI crystal of a crystalline toluene adductof the compound represented by Formula (I-3), and FIG. 7 is an X-raydiffraction diagram of a Type VII crystal of another crystalline tolueneadduct of the compound represented by Formula (I-3).

In each of the above drawings, axis of abscissa indicates angle ofdiffraction (2θ) and axis of ordinate indicates strength of diffraction.

FIG. 8 illustrates color density characteristics to temperature changeon the surface of heat-sensitive recording paper prepared using the TypeI crystalline form of the compound represented by Formula (I-1), theType II crystalline form of the crystalline toluene adduct of thecompound represented by Formula (I-1); and a known fluoran compound.

In FIG. 8, curve (a) illustrates color density characteristic of Type 1crystal; curve (a'), that of Type II crystal; curve (b), that of thecompound of Formula (A); curve (c), that of the compound of Formula (B);and curve (d), that of the compound of Formula (C), respectively.

FIG. 9 illustrates color density characteristics in relation ship totemperature change on the surface of heat-sensitive recording paperprepared using Type III crystal of the compound represented by Formula(I-2), using Type IV crystal of the crystalline toluene adduct of thecompound represented by formula (I-2), and using a known fluorancompound, respectively.

In FIG. 9, curve (e) illustrates the color density characteristic of theType III crystalline form, curve (e') illustrates that of the Type IVcrystalline form, and curve (f) illustrates that of the compound ofFormula (D).

FIG. 10 illustrates color density characteristics relative totemperature change on the surface of heat-sensitive recording paperprepared using the Type V crystalline form of the compound representedby formula (I-3), using the Type VI crystalline form of the crystallinetoluene adduct of the compound represented by the formula (I-3), usingthe Type VII crystalline form of another crystalline toluene adduct ofthe compound represented by Formula (I-3), and using a known fluorancompound.

In FIG. 10, curve (g) illustrates the color density characteristic ofthe Type V crystalline form, curve (g') illustrates that of the Type VIcrystalline form, curve (g") illustrates that of the Type VIIcrystalline form, and the curve (h) illustrates that of the compound offormula (E), respectively.

DETAILED DESCRIPTION OF THE INVENTION

The fluoran compounds of the present invention include compounds havingthe structural Formulas (I-1), (I-2) and (I-3): ##STR10##

The fluoran compounds of this invention can be prepared by reacting anbenzoic acid derivative represented by Formula (II): ##STR11## whereinR₁ and R₂ are the same as in Formula (I), e.g., compounds of formula(II-1), (II-2) or (II-3): ##STR12## with a diphenylamine derivativerepresented by Formula (III): ##STR13## wherein R₃ is a lower alkylgroup, in the presence of a dehydrating condensation agent, for example,concentrated sulfuric acid, mixture of oleum and concentrated sulfuricacid, polyphosphoric acid, phosphorus pentaoxide and anhydrous aluminumchloride, preferably concentrated sulfuric acid, and thereafter bringingthe reaction mixture to an alkaline pH.

The time and temperature of the dehydrating condensation reaction is notcritical and is usually carried out at 0° to 100° C. for from severalhours to 100 hours. When the reaction is carried out in concentratedsulfuric acid, the preferred reaction temperature is in the range of 0°to 50° C. The reaction time depends upon the selected reactiontemperature and hence the reaction is conducted for a sufficient time topermit the reaction to go to completion.

After the dehydrating condensation reaction is completed, the alkalitreatment is usually carried out by the addition of a base, e.g.,aqueous potassium hydroxide or sodium hydroxide solution to adjust thepH to an alkali value, e.g., 9 to 12. The treatment can be conducted inthe temperature range of 0° to 100° C. The alkali treatment may beconducted in the presence of an organic solvent other than water, forexample, benzene or toluene.

The benzoic acid derivative represented by Formula (II) can be preparedby reacting aminophenols, for example,3-N-cyclohexyl-N-n-butylaminophenol,3-N-cyclohexyl-N-isobutylaminophenol or3-N-n-butyl-N-isobutylaminophenol, with phthalic anhydride in theabsence or presence of a solvent such as benzene, toluene, xylene ortrichloroethylene. A Lewis acid, such as zinc chloride, may also beadded to the reaction.

Preferred examples of the diphenylamine derivatives represented byFormula (III) include compounds wherein R₃ is a lower alkyl group suchas methyl or ethyl. A particularly preferred diphenylamine derivative is4-methoxy-2-methyldiphenylamine, i.e., wherein R₃ is methyl.

The fluoran compounds of the present invention prepared by the aboveprocess can be obtained in a crystalline form which has a specific X-raydiffraction diagram by dissolving the desired product in an organicsolvent and precipitating in the form of crystals.

The crystalline form of a fluoran compound in the invention can beobtained by precipitating the product prepared by the above describedreaction as crystals from a solution thereof in an aromatic hydrocarbonsolvent such as benzene, an alcohol solvent such as methanol, ethanol,isopropanol and n-butanol, a polar solvent such as acetonitrile anddimethylformamide, or a mixture of these solvents, and isolating theprecipitated crystals.

A frequently employed method for precipitating the crystalline formthereof is to dissolve the fluoran compound completely in the solventand then cool the solution. The mixture of the fluoran compound and thesolvent may also be heated, if necessary, in the range of roomtemperature to the boiling point of the solvent in order to completelydissolve the fluoran compound. After dissolving completely, theresulting solution is then cooled with stirring or on standing toprecipitate the crystalline form of the compound.

Isolation of the precipitated crystal requires no specific procedure andcan be suitably carried out by known method such as filtration.

The crystalline solvated adducts of the fluoran compounds of the presentinvention, e.g., toluene adducts, can be obtained by using a solventwhich forms an adduct therewith, e.g., toluene, as the solvent forprecipitating the crystalline form of the compound.

For example, a crystalline toluene adduct of a fluoran compound of thepresent invention can be prepared by precipitating the fluoran compoundfrom a toluene-containing solvent.

Practical examples of toluene-containing solvents include toluene and asolvent mixture of toluene with one or more other solvents, for example,alcohols such as methanol and isopropanol, acetonitrile, andhydrocarbons such as n-hexane and benzene. The toluene content in thesolvent mixture is generally 2% by weight or more, preferably 5% byweight or more.

A method for precipitating the toluene adduct from a toluene-containingsolvent is to dissolve the fluoran compound in toluene or the solventmixture of toluene with other solvents and to precipitate thecrystalline toluene adduct by cooling the resultant solution to atemperature from 100° to -30° C., preferably from 80° to -5° C., withstirring or on standing. Additionally or alternatively, another solventin which the adduct is less soluble can be added to a toluene solutionof the fluoran compound to precipitate the crystalline adduct.

The crystalline forms of the fluoran compounds of the present inventionand the crystalline toluene adducts thereof will hereinafter beillustrated in detail.

The mole ratio of the fluoran compound to toluene in the crystallinetoluene adduct of the fluoran compound of the invention and X-raydiffraction diagrams of crystal powder are as described below.

The mole ratio of the fluoran compound to toluene was determined byelementary analysis and 'H-NMR spectrum analysis.

In the crystalline toluene adducts of the fluoran compound of Formula(I-1), the molar ratio of the fluoran compound to the toluene is from3:1.5 to 3:2.5.

FIG. 1 illustrates an X-ray diffraction diagram by Cu-Kα beams on apowder of the crystalline form of the fluoran compound of Formula (I-1)in non-solvated form (hereinafter referred to as Type I crystal).

FIG. 2 illustrates an X-ray diffraction diagram of a powder of acrystalline toluene adduct of the fluoran compound of formula (I-1)(hereinafter referred to as Type II crystal).

Type I crystals exhibit high peaks at the diffraction angle (2θ) of9.2°, 15.2°, 18.5°, 19.5°, 19.9° and 21.8°, and relatively high peaks at19.1° and 22.8° in the X-ray diffraction diagram by Cu-Kα beams asillustrated in FIG. 1. Type II crystals exhibit high peaks at thediffraction angle (2θ) of 5.5°, 9.5°, 17.7°, 18.7°, 19.1° and 19.6° ,and relatively high peaks at 11.8°, 15.3°, 21.0°, 23.4°, 23.7° and 24.2°in the X-ray diffraction diagram by Cu-Kα beams as illustrated in FIG.2. (Errors of about ±0.2° can be permitted in the indication ofdiffraction angle.)

Type I crystals have a melting point of 186° to 189° C., and Type IIcrystals have a melting point of 124° to 128° C.

The characteristics of these X-ray diffraction diagrams and thedifference in the melting points indicate that Type I crystals and TypeII crystals are distinctly different crystal forms.

In the crystalline toluene adducts of the fluoran compound of formula(I-2), molar ratio of the fluoran compound to the toluene is from 4:2.5to 4:3.5 moles.

FIG. 3 illustrates a X-ray diffraction diagram of the crystalline formof the fluoran compound of Formula (I-2) which is not solvated by asolvent such as toluene (hereinafter referred to as Type III crystal).

FIG. 4 illustrates a X-ray diffraction diagram of a crystalline tolueneadduct of the fluoran compound of Formula (I-2) (hereinafter referred toas Type IV crystal).

Type III crystals exhibit high peaks at the diffraction angle (2θ) of7.9° and 19.0°, and relatively high peaks at 17.0°, 20.3° and 24.1° inthe X-ray diffraction diagram by Cu-Kα beams as illustrated in FIG. 3.Type IV crystals exhibit a high peak at the diffraction angle (2θ) of6.0° and relatively high peaks at 11.2°, 13.3°, 16.4°, 18.5°, 19.0° and20.6° in the X-ray diffraction diagram by Cu-Kα beams as illustrated inFIG. 4.

Type III crystals have a melting point of 175° to 177° C. and Type IVcrystal has melting point of 123° to 126° C.

The characteristics of these X-ray diffraction diagrams and thedifference in the melting points indicate that Type III crystals andType IV crystals are definitely different crystal forms.

Further, the crystalline toluene adducts of the fluoran compound ofFormula (I-3) exist as two different crystal forms. These twocrystalline toluene adducts have a molar ratio of fluoran compound totoluene of 4:2.5 and 4:3.5, respectively.

FIG. 5 illustrates an X-ray diffraction diagram of the crystal offluoran compound of Formula (I-3) which is not solvated (hereinafterreferred to as Type V crystal).

FIG. 6 and FIG. 7 illustrate X-ray diffraction diagrams of the two kindsof crystalline toluene adducts of the compound of Formula (I-3)(hereinafter referred to as Type VI crystal and Type VII crystal,respectively).

Type V crystals exhibit high peaks at the diffraction angle (2θ) of6.7°, 11.6° and 20.7°, and relatively high peaks at 12.1°, 18.2° and21.3° in the X-ray diffraction diagram by Cu-Kα beams as illustrated inFIG. 5.

Type VI crystals exhibit a high peak at the diffraction angle (2θ) of5.7° and relatively high peaks at 17.8°, 18.7°, 20.3° and 24.4° in theX-ray diffraction diagram by Cu-Kα beams as illustrated in FIG. 6

Type VII crystals exhibit a high peak at 6.3° and relatively high peaksat 13.2°, 16.4° and 20.6° in the X-ray diffraction diagram by Cu-Kαbeams as illustrated in FIG. 7.

Type V crystals have a melting point of 147° to 149° C., Type VIcrystals have a melting point of 116° to 119° C., and Type VII crystalhave melting point of 95° to 98° C.

The characteristics of these X-ray diffraction diagrams and thedifference int h melting point sindicate that Type V crystal, Type VIcrystal and Type VII crystals are definitely different crystal forms.

The fluoran compounds of Formula (I), the crystalline forms thereof, andthe crystalline toluene adducts thereof can provide high solubility incapsule oil, an important property which is highly desired for thechromogenic compound of pressure-sensitive recording material, andprovides excellent weather resistance developed color image.

For example, the solubility of from Type I to Type VII crystalsdescribed above in commercial capsule oils were compared with knownfluoran compounds having the formulas (A), (B), (C), (D) and (E).respectively. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                                          SAS-296 80%                                 capsule oil    SAS-296  KMC-113   IP 20%                                      ______________________________________                                        Type I crystal ◯                                                                          ◯                                                                           ◯                               Type II crystal                                                                              ◯                                                                          ◯                                                                           ◯                               Type III crystal                                                                             ◯                                                                          ◯                                                                           ◯                               Type IV crystal                                                                              ◯                                                                          ◯                                                                           ◯                               Type V crystal ◯                                                                          ◯                                                                           ◯                               Type VI crystal                                                                              ◯                                                                          ◯                                                                           ◯                               Type VII crystal                                                                             ◯                                                                          ◯                                                                           ◯                               Compound of formula (A)                                                                      X        X         X                                           Compound of formula (B)                                                                      X        X         X                                           Compound of formula (C)                                                                      X        X         X                                           Compound of formula (D)                                                                      X        X         X                                           Compound of formula (E)                                                                      X        X         X                                           ______________________________________                                    

The method for determining the solubility is as follows. Each crystal orcompound is dissolved by heating at a concentration of 10% by weight inthe three capsule oils, respectively. After standing at 5° C. for aweek, the capsule oil is examined for precipitation of crystals. InTable ; ◯ means that no crystals are precipitated and x means thatprecipitation of crystals is observed.

SAS-296 is a capsule oil produced by Nippon Petrochemical Co., Ltd. andKMC-113 is a capsule oil produced by Kureha Chemical Industry Co., Ltd.IP is isoparaffine. The compound of Formula (A) cannot be completelydissolved even in hot KMC-113.

As clearly illustrated in Table 1, the fluoran compound represented byFormula (I), these compounds in crystalline form and the crystallinetoluene adducts of the fluoran compounds all have high solubility ineach capsule oil in cotrdistinction to the fluoran compounds of theformulas (A), (B), (C), (D) and (E).

These results mean that crystal precipitation does not occur duringstorage in the capsule oil in the preparation of the pressure-sensitiverecording material, and that crystal precipitation in the microcapsulesis not liable to occur after preparation of microcapsules. Such goodsolubility in the capsule oils is an important characteristic of thefluoran compounds of the present invention, including the crystallineforms thereof and the crystalline toluene adducts thereof very goodsolubility in a mixed oil of SAS 296 and IP-oil, in particular, meansthat cheaper capsule oil can also be employed, which circumstances areadvantageous in economy and industry.

The fluoran compounds of the invention, including the crystalline formsthereof and the crystalline toluene adducts thereof can provide aheat-sensitive recording paper which is free from soiling and has highwhiteness. The recording paper thus obtained can develop color morequickly at lower temperatures, compared with the compounds of formulas(A), (B), (C), (D) and (E). Hence the fluoran compounds of the presentinvention have extremely excellent properties in view of the presentdemand for high speed and high density recording materials.

The recording materials of the present invention are pressure-sensitiverecording material or heat-sensitive recording material which comprise afluoran compound of the present invention, e.g., a crystalline formthereof or a crystalline solvent e.g. toluene, adduct thereof.

The chromogenic compound employed therein can be a single fluorancompound or a mixture of fluoran compounds of the invention, e.g., as acrystalline form thereof and/or a crystalline solvent, e.g., toluene,adduct thereof. Further, in order to adjust the developed hue, otherchromogenic materials such as triphenylmethanlactones, fluorans andspiropiranes can also be added depending upon the demand.

When preparing pressure-sensitive recording material, a fluoran compoundof the invention, e.g., a crystalline form thereof or a crystallinetoluene adduct thereof, is dissolved in the selected solvent, i.e.,capsule oil. The solvent which is generally used in the field ofpressure sensitive recording includes single solvents and mixturethereof, for example, alkylbenzenes such as n-dodecylbenzene,alkylbiphenyls such as triethylbiphenyl and diisopropylbiphenyl,hydrogenated terphenyls, alkylnaphthalenes such asdiisopropylnaphthalene, diarylethanes such as phenylxylylethane andstyrenated ethylbenzene, and chlorinated paraffins. The resultingsolution is sealed by a coacervation method or an interfacialpolymerization method into microcapsules having an external wallcomprised of gelatin, melaminealdehyde resin, urea-aldehyde resin,polyurethane, polyurea, polyamide or the like. Aqueous dispersion of themicrocapsules is mixed with a suitable binder, such as starch paste andlatex, and applied to a suitable substrate such as paper, plastic sheetor resin coated paper. The coated back sheet for pressure-sensitiverecording is thus obtained.

The micro dispersion thus obtained can, of course, be used to Produceso-called middle-sheets wherein the microcapsule dispersion is appliedto one side of a substrate and a coating liquid primarily comprising adeveloper is applied to the other side of the substrate, and to produceso-called self contained sheets wherein both the microcapsules and thedeveloper are present on the same side of a substrate.

The self contained sheet is prepared by applying a coating liquidcomprising the microcapsules and the developer to one side of thesubstrate or by applying a microcapsules dispersion to one side of thesubstrate and then applying a coating liquid of the developer on thecoated layer of the microcapsules.

Exemplary developer suitable for use in the pressure-sensitive recordingmaterial includes copolymers of salicylic acid, phenols and aldehydessuch as form aldehyde; alkyl, aryl or aralkyl substituted salicylic acidsuch as 3,5-di-α-methylbenzylsalicylic acid; polycondensate ofsubstituted salicylic acid and styrene; alkylphenols such asoctylphenol; phenol aldehyde resin, such as p-phenylphenol novolakresin; metal salts of these compounds such as zinc, magnesium, aluminum,calcium, tin and nickel salts; and activated clays.

When preparing a heat-sensitive recording material of the invention, afluoran compound of the invention, e.g., a crystalline form thereof or acrystalline toluene adduct thereof is pulverized in water to form anaqueous dispersion. The dispersion is mixed with an aqueous dispersionof pulverized developer, and binder is added to the thus obtainedmixture.

Representative examples of developers which are suitable for use in theheat sensitive recording material include bisphenol A, halogenatedbisphenol A, alkylated bisphenol A, dihydroxydiphenyl sulfone,halogenated dihydroxydiphenyl sulfone, alkylated dihydroxydiphenylsulfone, hydroxybenzoic acid esters, hydroquinone monoethers and otherphenol derivatives; organic developers such as salicylic acidderivatives, salicylamide derivatives, urea derivatives, and thioureaderivatives; and inorganic developers such as acid clay, attapulgite,activated clay, aluminum chloride and zinc bromide.

Exemplary binder used for the heat-sensitive recording material includespolyvinyl alcohol, modified polyvinyl alcohol, methylcellulose,hydroxyethylcellulose, carboxymethylcellulose, gum arabic, salt ofstyrene-maleic anhydride copolymer, and isobutyleneacrylic acid-maleicanhydride copolymer.

Other additives can also be employed. Exemplary additives includefillers such as talc, kaolin and calcium carbonate, and if necessary,may also include sensitizers such as higher fatty acid amides, aromaticcarboxylic acid esters, aromatic sulfonic acid esters, aromatic ethers,aromatic substituted aliphatic ethers, aromatic hydrocarbons, aromaticsubstituted aliphatic hydrocarbons and other generally known sensitizersfor the heat-sensitive recording material; UV-absorbers; and defoamers.

The coating liquid obtained by the addition of the above additives canbe applied to a suitable substrate such as paper, plastic sheet andresin coated paper and used as the heat-sensitive recording material.The heat-sensitive recording system of the invention can of course beused in a solvent system without any problem in place of the aboveaqueous dispersion system. The system of the invention can also beemployed for other enduse applications using chromogenic materials, forexample, a temperature-indicating material.

The color density characteristics dependent upon the temperature changewere measured on the heat-sensitive recording material of the presentinvention, that is, a heat-sensitive recording paper obtained by usingthe crystalline form and the crystalline toluene adduct of a fluorancompound represented by the formula (I) as the chromogenic compound andusing bisphenol A as the developer. The results are illustrated in FIGS.8, 9 and 10. Color density was measured with a Macbeth reflectiondensitometer (Model; TR-524). Larger values indicate higher density ofdeveloped color.

FIG. 8 illustrates the color density characteristics depending upontemperature change for Type I and Type II crystals of the invention andreference compounds of Formulas (A), (B) and (C), FIG. 9 illustrates thesame relationship on Type III and Type IV crystals of the invention anda reference compound of Formula (D), and FIG. 10 illustrates the samerelationship on Type V, Type VI and Type VII crystals of the presentinvention and a reference compound of Formula (E), respectively.

FIG. 8 illustrates that Type I and Type II crystals of the inventionhave the excellent characteristic of developing color more quickly atlower temperatures as compared with the compounds of Formulas (A), (B)and (C). FIG. 9 illustrates that Type III and Type IV crystals of theinvention have the excellent characteristic of developing color morequickly at lower temperatures as compared with the compounds of Formulas(C) and (D). FIG. 10 illustrates that Type V, Type VI and Type VIIcrystals of the invention have the excellent characteristic ofdeveloping color more quickly at lower temperatures as compared with thecompounds of Formulas (A), (B) and (D).

In order to develop color at lower temperatures, a sensitizer which is aheat-fusible substance having a relatively low melting point of about100° C. is commonly used in addition to the chromogenic compound and thedeveloper. On the other hand, a fluoran compound represented by theformula (I) of the invention, e.g., a crystalline form thereof or acrystalline toluene adduct thereof, has the remarkable advantage thatcolor development can be quickly achieved at lower temperature in theabsence of the sensitizer or in the presence of a smaller amount of thesensitizer as compared to using a compound of Formulas (A), (B), (C),(D) or (E).

The fluoran compounds of Formula (I) differs from the fluoran compoundsof Formulas (A), (B), (C), (D) and (E) only in the substituent on theamino group at the 3 position of the fluoran structure. For example, thecompounds of Formula (I-1) and Formula (I-2) differ from the methylaminosubstituted compound of 3 position of Formula (C) or the isoamylaminosubstituted compound of formula (D) by an n butylamino or anisobutylamino group, respectively. Similarly, the compound of Formula(I-3) differs from the compound of Formula (B) by one of the butylgroups on the amino group at the 3 position being isobutyl instead ofn-butyl. Although these differences in chemical structure are small, asmentioned above, the fluoran compounds of the present invention haveextremely outstanding characteristics as the chromogenic compound, forexample, solubility in capsule oils and heat-sensitive color developingcharacteristics.

The present invention will hereinafter be illustrated further in detailby way of examples. However, it is to be understood that the inventionis not intended to be limited to the specific embodiments.

EXAMPLE 1 [Preparation of Type I crystals of the fluoran compound offormula (I-1)]

After dissolving 20 g of2-(4'-N-cyclohexyl-N-n-butylamino-2'-hydroxybenzoyl)benzoic acid, i.e.,the compound of Formula (II-1), in 100 ml of concentrated sulfuric acidat 10° C., 11 g of 4-methoxy-2-methyldiphenylamine, i.e., the compoundof Formula (III) wherein R₃ is methyl, was added at the same temperatureand stirred at 10° to 25° C. for 48 hours. The reaction mixture waspoured into 600 ml of ice water. The separated solid was collected,washed with water and added to 500 ml of a 10% aqueous sodium hydroxidesolution, and stirred at 60° to 70° C. for 2 hours. Thereafter the solidwas filtered, washed with water and further washed with 100 ml ofisopropanol.

The resulting solid was recrystallized twice with n-butanol to obtain 20g of the desired 3-N-cyclohexyl-N-n-butylamino-6-methyl-7-anilinofluoranas almost colorless crystals. Yield was 67% and melting point was 186°to 189° C.

A toluene solution of the compound thus obtained was colorless andtransparent. A reddish black color quickly developed on silica gel. Thecompound had a maximum absorption at a wave length of 455 nm and 594 nmin a 95% aqueous acetic acid solution. An X-ray diffraction diagram ofthe powder of these crystals is illustrated in FIG. 1.

EXAMPLE 2 [Preparation of Type II crystals of a crystalline tolueneadduct of the fluoran compound of Formula (I-1)]

After dissolving 200 g of2-(4'-N-cyclohexyl-N-n-butylamino-2'-hydroxybenzoyl)benzoic acid in 600ml of concentrated sulfuric acid at 10° C., 110 g of4-methoxy-2-methyldiphenylamine was added at the same temperature andstirred at 10° to 25° C. for 48 hours.

The reaction mixture was poured into 6000 ml of ice water. The separatedsolid was collected, washed with water and added to 1000 ml of a 20%aqueous sodium hydroxide solution. A further 1000 ml of toluene wasadded to the resultant mixture and stirred at 60° to 70° C. for 2 hours.

The toluene layer was separated and washed with warm water until thewater became neutral after washing. The toluene solution thus obtainedwas concentrated at 40° C. under reduced pressure. The separatedcrystals were filtered, washed with a small amount of toluene, furtherwashed with methanol and dried at 40° C. for 18 hours to obtain 250 g oftoluene adduct of3-N-cyclohexyl-N-n-butylamino-6-methyl-7-anilinofluoran as almostcolorless crystals. Melting point was 124° to 128° C.

Elementary analysis (3·C₃₇ H₃₈ O₃ N₂ :2·C₇ H₈)

    ______________________________________                                                   C         H      N                                                 ______________________________________                                        Calculated (%)                                                                             80.70       7.04   4.52                                          Found (%)    80.83       7.02   4.75                                          ______________________________________                                    

A toluene solution of the compound thus obtained was colorless andtransparent. A reddish black color quickly developed on silica gel. Thecompound had a maximum absorption at a wave length of 455 nm and 594 nmin a 95% aqueous acetic acid solution. An X-ray diffraction diagram ofthe powder is illustrated in FIG. 2.

EXAMPLE 3 [preparation of Type II crystals of a crystalline tolueneadduct of the fluoran compound of Formula (I-1)]

After dissolving 20 g of2-(4'-N-cyclohexyl-N-n-butylamino-2'-hydroxybenzoyl)benzoic acid in 100ml of concentrated sulfuric acid at 10° C., 11 g of4-methoxy-2-methyldiphenylamine was added at the same temperature andstirred at 10° to 25° C. for 48 hours.

The reaction mixture was poured into 600 ml of ice water. The separatedsolid was collected, washed with water and added to 500 ml of a 10%aqueous sodium hydroxide solution. A further 300 ml of toluene was addedto the resultant mixture and stirred at 60° to 70° C. for 2 hours.

The toluene layer was separated and washed with warm water until thewater became neutral after washing. Thereafter 280 ml of toluene wasdistilled off from the toluene solution at 50° C. under reducedpressure. The residual viscous oil was mixed with 300 ml of methanol toprecipitate crystals. The desired toluene adduct of 3 Ncyclohexyl-N-n-butylamino-6-methyl-7-anilinofluoran thus obtained was 22g. The adduct was almost colorless crystals and had a melting point of124° to 128° C.

EXAMPLE 4 [Preparation of Type I crystals from Type II crystals]

After dissolving 20 g of Type II crystals of Example 2 in 100 ml ofacetonitrile, the solution obtained was cooled to the room temperature.The crystals which separated were filtered to obtain 17 g of Type Icrystals. Melting point was 186° to 189° C.

EXAMPLE 5 [Preparation of Type III crystals of the fluoran compound ofFormula (I-2)]

After dissolving 100 g of2-(4'-N-cyclohexyl-N-isobutylamino-2'-hydroxybenzoyl)benzoic acid in 300ml of concentrated sulfuric acid at 10° C., 53 g of4-methoxy-2-methyldiphenylamine was added at the same temperature andstirred at 10° to 25° C. for 48 hours.

The reaction mixture was poured into 1500 ml of ice water the separatedsolid was collected, washed with water and added to 1000 ml of a 10%aqueous sodium hydroxide solution. A further 800 ml of toluene was addedto the resultant mixture and stirred at 60° to 70° C for 2 hours. Thetoluene layer was separated and washed with warm water until the waterbecame neutral after washing. The toluene solution thus obtained wasconcentrated to 200 ml by distilling off toluene at 50° C. under reducedpressure and allowed to cool to room temperature.

The precipitated crystals were filtered, slurried with 1000 ml ofmethanol and washed with 500 ml of methanol to obtain 88 g of3-N-cyclohexyl-N-isobutylamino-6-methyl-7-anilinofluoran. Yield was 62%and melting point was 175° to 177° C. A toluene solution of the compoundwas colorless and transparent. A reddish black color quickly developedon silica gel. The compound had a maximum absorption at a wave length of455 nm and 595 nm in a 95% aqueous acetic acid solution. The X-raydiffraction diagram of the powder is illustrated in FIG. 3.

EXAMPLE 6 [Preparation of Type IV crystals of crystalline toluene adductof the fluoran compound of Formula (I-2)]

After dissolving 100 g of2-(4'-N-cyclohexyl-N-isobutylamino-2'-hydroxybenzoyl)benzoic acid in 300ml of concentrated sulfuric acid at 10° C., 53 g of4-methoxy-2-methyldiphenylamine was added at the same temperature andstirred at 10° to 25° C. for 48 hours.

The reaction mixture was poured into 1500 ml of ice water. The separatedsolid was collected, washed with water and added to 1000 ml of a 10%aqueous sodium hydroxide solution. A further 800 ml of toluene was addedto the resultant mixture and stirred at 60° to 70° C. for 2 hours.

The toluene layer was separated and washed with warm water until thewater became neutral after washing. Thereafter the toluene solution wasconcentrated to 200 ml at 50° C. under reduced pressure. After allowedto cool to room temperature, the crystals which separated were filtered,washed with a small amount of toluene, and dried to obtain 100 g oftoluene adduct of3-N-cyclohexyl-N-iso-butylamino-6-methyl-7-anilinofluoran as almostcolorless crystals. Melting point was 123° to 126° C.

Elementary analysis (4·C₁₇ H₃₈ O₃ N₂ :3·C₇ H₈)

    ______________________________________                                                   C         H      N                                                 ______________________________________                                        Calculated (%)                                                                             80.83       7.06   4.46                                          Found (%)    80.75       7.07   4.51                                          ______________________________________                                    

A toluene solution of the compound thus obtained was colorless andtransparent. A reddish black color was quickly developed on silica gel.The compound had a maximum absorption at a wave length of 455 nm and 595nm in a 95% aqueous acetic acid solution. The X-ray diffraction diagramof the powder is illustrated in FIG. 4.

EXAMPLE 7 [Preparation of Type III crystals from Type IV crystals]

After dissolving 20 g of Type IV crystals, prepared as described inExample 6, in 100 ml of methanol by heating, the solution was cooled toroom temperature. Separated crystals were filtered to obtain 15 g ofType III crystals. Melting point was 175 to 177° C.

EXAMPLE 8 [Preparation of Type V crystals of the fluoran compound ofFormula (I-3)]

After dissolving 29.5 g of2-(4'-N-n-butyl-N-isobutylamino-2'-hydroxybenzoyl)benzoic acid in 100 mlof concentrated sulfuric acid at 10° C., 17 g of4-methoxy-2-methyldiphenylamine was added at the same temperature andthe mixture was stirred at 10° to 25° C. for 48 hours.

The reaction mixture was poured into 600 ml of ice water. The separatedsolid was collected, washed with water and added to 500 ml of a 10%aqueous sodium hydroxide solution. The mixture was stirred at 60° to 70°C. for 2 hours. The solid was filtered, washed with water, washed with100 ml of isopropanol and further recrystalized twice from isopropanolto obtain 26 g of 3-N-n-butyl-N-isobutylamino-6-methyl-7-anilinofluoranas almost colorless crystals. Yield was 62%. Melting point was147°-149°.

A toluene solution of the compound thus obtained was colorless andtransparent. A reddish black color was quickly developed on silica gel.The compound had a maximum absorption at a wave length of 452 nm and 594nm in a 95% aqueous acetic acid solution. The X-ray diffraction diagramof the powder is illustrated in FIG. 5.

EXAMPLE 9 [Preparation of Type VI crystals of crystalline toluene adductof the fluoran compound of Formula (I-3)]

After dissolving 29.5 g of2-(4'-N-n-butyl-N-isobutylamino-2'-hydroxybenzoyl)benzoic acid in 100 mlof concentrated sulfuric acid at 10° C., 17 g of4-methoxy-2-methyldiphenylamine was added at the same temperature andthe mixture was stirred at 10° to 25° C. for 48 hours.

The reaction mixture was poured into 600 ml of ice water. The separatedsolid was collected, washed with water and added to 500 ml of a 10%aqueous sodium hydroxide solution. A further 300 ml of toluene was addedto the resultant mixture, which was then stirred at 60° to 70° C. for 2hours.

The toluene layer was separated and washed with warm water until thewater becomes neutral after washing. Thereafter 280 ml of toluene wasdistilled Off at 50° C. under reduced pressure. The residual viscous oilwas crystallized by mixing with 300 ml of methanol to obtain 35.3 g oftoluene adduct of 3-N-n-butyl-N-isobutylamino-6-methyl-7-anilinofluoranas almost colorless crystals. Melting point was 116° to 119° C.

Elementary analysis (3·C₃₅ H₃₆ O₃ N₂ :2·C₇ H₈)

    ______________________________________                                                   C         H      N                                                 ______________________________________                                        Calculated (%)                                                                             80.19       7.01   4.72                                          Found (%)    79.96       6.93   4.87                                          ______________________________________                                    

A toluene solution of the compound thus obtained was colorless andtransparent. A reddish black color was quickly developed on silica gel.The compound had a maximum absorption at a wave length of 452 nm and 594nm in a 95% aqueous acetic acid solution. The X-ray diffraction diagramof the powder is illustrated in FIG. 6.

EXAMPLE 10 [Preparation of Type VII crystals of crystalline tolueneadduct of the fluoran compound of Formula (I-3)]

After dissolving 100 g of2-4'-N-n-butyl-N-isobutylamino-2'-hydroxybenzoyl)benzoic acid in 330 mlof concentrated sulfuric acid at 10° C., 58 g of4-methoxy-2-methyldiphenylamine was added at the same temperature andstirred at 10° to 25° C. for 48 hours.

The reaction mixture was poured into 2000 ml of ice water. The separatedsolid was collected, washed with water and added to 1500 ml of a 10%aqueous sodium hydroxide solution. A further 1000 ml of toluene wasadded to the resultant mixture, which was then stirred at 60° to 70° C.for 2 hours.

The toluene layer was separated and washed with warm water until thewater becomes neutral after washing. Thereafter the toluene layer wasallowed to stand at room temperature. The precipitated crystals werefiltered, washed with a small amount of toluene, further washed withmethanol and dried to obtained 115 g of the toluene adduct of3-N-n-butyl-N-iso-butylamino 6-methyl-7-anilinofluoran as almostcolorless crystals. Melting point was 95 to 98° C.

Elementary analysis (3·C₃₅ H₃₆ O₃ N₂ :2·C₇ H₈)

    ______________________________________                                                   C         H      N                                                 ______________________________________                                        Calculated (%)                                                                             80.19       7.01   4.72                                          Found (%)    80.10       6.97   4.70                                          ______________________________________                                    

A toluene solution of the compound thus obtained was colorless andtransparent. A reddish black color was quickly developed 0n silica gel.The compound had a maximum absorption at a wave length of 452 nm and 594nm in a 95% aqueous acetic acid solution. The X-ray diffraction diagramof the powder is illustrated in FIG. 7.

EXAMPLE 11 [Preparation of Type V crystals from Type VI crystals]

After dissolving 20 g of Type VI crystals, prepared as described inExample 9, in 180 ml of isopropanol by heating, the solution was cooledto the room temperature. Separated crystals were filtered to obtain 17 gof Type V crystals. Melting point was 147° to 149° C.

EXAMPLE 12 [Preparation of Type V crystals from Type VII crystals]

After dissolving 20 g of Type VII crystals prepared in Example 10 in 180ml of isopropanol by heating, the solution was cooled to the roomtemperature. The crystals which separated were filtered to obtain 17 gof Type V crystals. Melting point was 147° to 149° C.

EXAMPLE 13 [Preparation of heat-sensitive recording paper using Type Icrystals of the compound of Formula (I-1)]

A mixture of 10 g of Type I crystals of the compound represented byFormula (I-1), 5 g of 10% aqueous polyvinyl alcohol solution and 37.5 gof water was pulverized to a particle size of 3 μ using a sand mill.Separately, bisphenol A was dispersed in a similar manner to obtain a38% dispersion of developer. Then 65.8 g of the developer dispersionthus obtained, 50.9 of the above aqueous dispersion of Type I crystals,18.3 g of 60% aqueous precipitated calcium carbonate dispersion, 88 g of10% aqueous polyvinyl alcohol solution and 51.9 g of water were mixed.

The thus-obtained mixture was applied on a white base paper by using awire rod No. 10 and air-dried at the room temperature to obtain anextremely white heat-sensitive recording paper which was free fromsoiling. When the heat-sensitive recording paper thus obtained washeated, a slightly reddish black color was very quickly developed.

The color density characteristics of the heat-sensitive recording paperto temperature change was measured with RHODIACETA™ (LYON, FRANCE). Theresults are illustrated in FIG. 8.

Color density was measured with a Macbeth reflection densitometer ModelTR-524. A larger value indicates higher color density.

EXAMPLE 14 [Preparation of heat-sensitive recording paper using Type IIcrystals of the crystalline toluene adduct of the compound of Formula(I-1)]

A heat sensitive recording paper was prepared carrying out the sameprocedures as described in Example 13 except that Type II crystals ofthe crystalline toluene adduct of the compound of Formula (I-1) wereused in place of Type crystals of the compound of Formula (I-1).

A slightly reddish black color was very quickly developed by heating theheat-sensitive recording paper thus obtained.

The color density characteristics of the heat-sensitive recording paperto temperature change was measured with RHODIACETA™ (LYON, FRANCE). Theresult are illustrated in FIG. 8.

EXAMPLE 15 [Preparation of heat-sensitive recording paper using Type IIIcrystals of the compound of Formula (I-2)]

A heat-sensitive recording paper was prepared carrying out the sameprocedures as described in Example 13 except that Type III crystals ofthe compound of Formula (I-2) were used in place of Type I crystals ofthe compound of Formula (I-1).

A slightly reddish black color was very quickly developed by heating theheat sensitive recording paper thus obtained.

The color density characteristics of the heat-sensitive recording paperto temperature change was measured with RHODIACETA™ (LYON, FRANCE). Theresults are illustrated in FIG. 9.

EXAMPLE 16 [Preparation of heat-sensitive recording paper using Type IVcrystals of the crystalline toluene adduct of the compound of Formula(I-2)]

A heat-sensitive recording paper was prepared carrying out the sameprocedures as described 1n Example 13 except that Type IV crystals ofthe crystalline toluene adduct of the compound of Formula (I-2) wereused in place of Type I crystals of the compound of Formula (I-1).

A slightly reddish black color was very quickly developed by heating theheat-sensitive recording paper thus obtained.

The color density characteristics of the heat-sensitive recording paperto temperature change was measured with RHODIACETA™ (LYON, FRANCE). Theresults are illustrated in FIG. 9.

EXAMPLE 17 [Preparation of heat-sensitive recording paper using Type Vcrystals of the compound of Formula (I-3)]

A heat-sensitive recording paper was prepared carrying out the sameprocedures as described in Example 13 except that Type V crystals of thecompound of Formula (I-3) were used in place of Type I crystals of thecompound of Formula (I-1).

A slightly reddish black color was very quickly developed by heating theheat-sensitive recording paper thus obtained.

The color density characteristics of the heat-sensitive recording paperto temperature change was measured with RHODIACETA™ (LYON, FRANCE). Theresults are illustrated in FIG. 10.

EXAMPLE 18 [Preparation of heat-sensitive recording paper using Type VIcrystals of the crystalline toluene adduct of the compound of Formula(I-3)]

A heat-sensitive recording paper was prepared carrying out the sameprocedures as described in Example 13 except that Type VI crystals ofthe crystalline toluene adduct of the compound of Formula (I-3) wereused in place of Type I crystals of the compound of Formula (I-1).

A slightly reddish black color was very quickly developed by heating theheat-sensitive recording paper thus obtained.

The color density characteristics of the heat-sensitive recording paperto temperature change was measured with RHODIACETA™ (LYON, FRANCE). Theresult are illustrated in FIG. 10.

EXAMPLE 19 [Preparation of heat-sensitive recording paper using Type VIIcrystals of the Crystalline toluene adduct of the compound of Formula(I-3)]

A heat-sensitive recording paper was prepared by carrying out the sameprocedures as described in Example 13 except that Type VII crystals Ofthe crystalline toluene adduct of the compound of Formula (I-3) wereused in place of Type I crystals of the compound represented by theformula (I-1).

A slightly reddish black color very quickly developed by heating theheat-sensitive recording paper thus obtained.

The color density characteristics of the heat-sensitive recording paperto temperature change was measured with RHODIACETA™ (LYON, FRANCE). Theresults are illustrated in FIG. 10.

COMPARATIVE EXAMPLE

Heat-sensitive recording papers were prepared carrying out the sameprocedures as described in Example 13 except that Type I crystals of thecompound of Formula (I-1) were replaced by3-N,N-diethylamino-6-methyl-7-anilinofluoran [compound of Formula (A)],3-N,N-di-n-butylamino-6-methyl-7-anilinofluoran [compound of Formula(B)], 3-N-cyclohexyl-N-methylamino-6-methyl-7-anilinofluoran [compoundof Formula (C)], 3-N-cyclohexyl-N-isoamylamino-6-methyl-7-anilinofluoran[compound of Formula (D), and3-N-isobutyl-N-ethyl-6-methyl-7-anilinofluoran [compound of Formula(E)], respectively. Color density characteristics to temperature changewere measured. Results are illustrated in FIGS. 8, 9 and 10.

Additionally, the surface of the heat-sensitive recording paper to whichthe compound of the formula (A) was applied had somewhat greyish colorand greasing was observed.

EXAMPLE 20 [Preparation of pressure-sensitive recording paper using TypeI crystal of the compound of Formula (I-1)]

Coated back sheet (CB) and coated front sheet (CF) were prepared by thefollowing procedures.

A mixture of 100 g of a 10% aqueous solution of ethylenemaleic anhydridecopolymer and 240 g of water was adjusted to PH 4.0 with a 10% aqueoussodium hydroxide solution and mixed with 200 g of a solution containing5% by weight of Type I crystals of the compound of Formula (I-1) inphenylxylylethane (SAS-296; Trade Mark of a product of NipponPetrochemical Co., Ltd.). After emulsifying the resultant mixture with ahomomixer, 60 g of an aqueous methylolmelamine solution containing 50%of solid (Uramine T-30; Trade Mark of a product of Mitsui ToatsuChemicals Inc.) was added, and stirred at 55° C. for 3 hours to obtain amicrocapsule dispersion having an average particle size of 5.0 μ.

To 100 g of the microcapsule dispersion, 4.0 g of wheat starch, 20 g of20% paste of oxidized starch and 116 g of water were added anddispersed. The dispersion thus obtained was applied on a paper having abasis weight of 40 g/m² so as to obtain a coating weight of 5 g/m² assolid, CB sheet was thus obtained.

On the other hand, in order to prepare CF sheet, the zinc salt of asubstituted salicylic acid styrene copolymer was pulverized in waterwith a sand grinding mill in the presence of a small amount of a highmolecular weight anionic surfactant to obtain an aqueous dispersion witha 40% by weight solids content. Using the aqueous dispersion, a coatingcompound (30% solid content) having the below described composition wasprepared and applied on a woodfree paper having a basis weight of 40g/m² so as to obtain a coating wight of 5.5 g/m². A CF sheet was thusobtained.

    ______________________________________                                                            Weight of solid                                           Aqueous Coating Composition                                                                       (g)                                                       ______________________________________                                        Precipitated calcium carbonate                                                                    100                                                       Developer           20                                                        Binder (Starch)     8                                                         (Synthetic latex)   8                                                         ______________________________________                                    

The microcapsule coated CB sheet and the developer coated CF sheet wereoverlapped so as to bring both coated surfaces into contact with eachother. When pressure was applied on the overlapped sheets with a pencil,a reddish black image emerged on the developer coated surface. Thedeveloped color image had practically no problems with respect toresistance to light, moisture and NO_(x).

EXAMPLE 21 [Preparation of pressure-sensitive recording paper using TypeII crystals of crystalline toluene adduct of the compound of Formula(I-1)]

A CB sheet and a CF sheet were prepared carrying out the same proceduresas described in Example 20 except that Type II crystals of thecrystalline toluene adduct of the compound of formula (I-1) were used inplace of the Type I crystals of the compound of Formula (I-1). A colorimage was developed by the same procedures as in Example 20. Thedeveloped color image had practically no problems with respect toresistance to light, moisture and No_(x).

EXAMPLE 22 [Preparation of pressure-sensitive recording paper using TypeIII crystals of the compound of Formula (I-2)]

A CB sheet and a CF sheet were prepared carrying out the same proceduresas described in Example 20 except that Type III crystals of the compoundrepresented by the formula (I-2) were used in place of the Type Icrystals of the compound of Formula (I -2). A color image was developedby the same procedures as in Example 20. The developed color image hadpractically no problems with respect to resistance to light, moistureand No_(x).

EXAMPLE 23 [Preparation of pressure-sensitive recording paper using TypeIV crystals of crystalline toluene adduct of the compound of Formula(I-2)]

A CB sheet and a CF sheet were prepared carrying out the same proceduresas described in Example 20 except that Type IV crystals of thecrystalline toluene adduct of the compound of Formula (I-2) were used inplace of the Type I crystals of the compound of Formula (I-1). A colorimage was developed by the same procedures as in Example 20. Thedeveloped color image had practically no problem on the resistance tolight, moisture and NO_(x).

EXAMPLE 24 [Preparation of pressure-sensitive recording paper using TypeV crystals of the compound of Formula (I-3)]

A CB sheet and a CF sheet were prepared carrying out the same proceduresas described in Example 20 except that Type V crystals of the compoundof Formula (I-3) were used in place of the Type I crystals of thecompound of Formula (I-1). A color image was developed by the sameprocedures as in Example 20. The developed color image had practicallyno problem on the resistance to light, moisture and NO_(x).

EXAMPLE 25 [Preparation of pressure-sensitive recording paper using TypeVI crystals of crystalline toluene adduct of the compound of Formula(I-3)]

A CB sheet and a CF sheet were prepared carrying out the same proceduresas described in Example 20 except that Type VI crystals of thecrystalline toluene adduct of the compound Of Formula (I-3) were used inplace of the Type I crystals of the compound of Formula (I-1). A colorimage was developed by the same procedures as in Example 20. Thedeveloped color image had practically no problems with respect toresistance to light, moisture and NO_(x).

EXAMPLE 26 [Preparation of pressure-sensitive recording paper using TypeVII crystals of crystalline toluene adduct of the compound of Formula(I-3)]

A CB sheet and a CF sheet were prepared carrying out the same proceduresas described in Example 20 except that Type VII crystals of thecrystalline toluene adduct of the compound of Formula (I-3) were used inplace of the Type I crystals of the compound of Formula (I-1). A colorimage was developed by the same procedures as in Example 20. Thedeveloped color image had practically no problems with respect toresistance to light, moisture and NO_(x).

What is claimed is:
 1. A recording material comprising a support having at least one layer therein containing a chromogenic fluoran compound of the formula (I) ##STR14## wherein R₁ and R₂ are different groups and are selected form cyclohexyl, n-butyl and isobutyl.
 2. The recording material of claim 1, wherein in the fluoran compound of formula (I) R₁ is cyclohexyl and R₂ is n-butyl.
 3. The recording material of claim 1, wherein in the fluoran compound of formula (I) R₁ is cyclohexyl and R₂ is isobutyl.
 4. The recording material of claim 1, wherein in the fluoran compound of formula (I) R₁ is n-butyl and R₂ is isobutyl.
 5. The recording material of claim 1, wherein the fluoran compound of formula (I) is in crystalline form.
 6. The recording material of claim 5, wherein in the fluoran compound of formula (I) R₁ is cyclohexyl and R₂ is n-butyl, and the X-ray diffraction diagram by Cu-K α beams of the crystalline form of the fluoran compound indicates a high peak at a diffraction angle 2θ of 9.2°, 15.2°, 18.5°, 19.5°, 19.9° and 21.8`, and a relatively high peak at 19.1° and 22.8°.
 7. The recording material of claim 5, wherein in the fluoran compound of formula (I) R₁ is cyclohexyl and R₂ is isobutyl, and the X-ray diffraction diagram by Cu-Kα beams of the crystalline form of the fluoran compound indicates a high peak at a diffraction angle 2θ of 7.9° and 19.0° and a relatively high peak at 17.0°, 20.3° and 24.1°.
 8. The recording material of claim 5, wherein in the fluoran compound of formula (I) R₁ is n-butyl and R₂ is isobutyl, and the X-ray diffraction diagram by Cu-K α beams of the crystalline form of the fluoran compound indicates a high peak at a diffraction angle 2θ of 6.7°, 11.6°, and 20.7°, and a relatively high peak at 12.1°, 18.2° and 21.3°.
 9. The recording material of claim 1, wherein the fluoran compound of formula (I) is in the form of a crystalline toluene adduct.
 10. The recording material of claim 9, wherein in the fluoran compound of formula (I) R₁ is cyclohexyl and R₂ is n-butyl and the X-ray diffraction diagram by Cu-Kα beams of the crystalline form of the fluoran compound indicates a high peak at a diffraction angle 2θ of 5.5°, 9.5°, 17.7°, 18.7°, 19.1° and 19.6°, and a relatively high peak at 11.8°, 15.3°, 21.0°, 23.4°, 23.7° and 24.2°.
 11. The recording material of claim 9, wherein in the fluoran compound of formula (I) R₁ is cyclohexyl and R₂ is isobutyl and the X-ray diffraction diagram by Cu-Kα beams of the crystalline form of the fluoran compound indicates a high peak at a diffraction angle 2θ of 6.0°, and a relatively high peak at 11.2°, 13.3°, 16.4°, 18.5°, 19.0° and 20.6°.
 12. The recording material of claim 9, wherein in the fluoran compound of formula (I) R₁ is n-butyl and R₂ is isobutyl, and the X-ray diffraction diagram by Cu-Kα beams of the crystalline form of the fluoran compound indicates a high peak at a diffraction angle 2∝ of 5.7° and a relatively high peak at 17.8°, 18.7°, 20.3° and 24.4°.
 13. The recording material of claim 9, wherein in the fluoran compound of formula (I) R₁ is n-butyl and R₂ is isobutyl, and the X-ray diffraction diagram by Cu-Kα beams of the crystalline form of the fluoran compound indicates a high peak at a diffraction angle 2∝ of 6.3° and a relatively high peak at 13.2°, 16.4°, 20.3° and 20.6°. 